How do I extract files from an MSI package?

First, access an elevated command prompt, to do this:

1. Click the Start button.

2. Click All Programs.

3. Go into Accessories.

4. Right-click on Command Prompt.

5. Select Run as administrator.

6. When the UAC Prompt appears, click Continue.

Once you have your elevated command prompt, input the following:

msiexec /a drive:\filepath\to\MSI\file /qb TARGETDIR=drive:\filepath\to\target\folder

using the desired locations to fill the above mentioned filepaths. Example:

msiexec /a c:\testfile.msi /qb TARGETDIR=c:\temp\test

Use 7Zip.
It will unpack MSI , CAB, some EXE, and a lot more packages for you .There is no need for admin privileges to run this either.

-EDIT-

And its open source, so no nagging messages begging you to buy the stuff

There is also lessmsi which is completely free and open source.

There are no advertisements or nagging messages, it will preserve directory structure and file names correctly, has a sophisticated command line interface, as well as a graphical user interface that allows browsing through the files as well as viewing internal MSI tables and other MSI attributes.